DES MOINES, Iowa _ In the closest finish in the history of the Iowa caucuses, Mitt Romney edged out Rick Santorum by eight votes in the first battle for the Republican presidential nomination.

A distant fifth-place finish apparently ended the once-promising candidacy of Rick Perry. The Texas governor, who started as a prime contender for the nomination last summer, broke off plans to fly to South Carolina for more campaigning, and said he was returning home instead to "determine whether this is a path forward."

Santorum rode a late-breaking burst of support after getting counted out by virtually everyone until the final days of a long campaign. His Iowa comeback represented a drastic reversal from his last election night, a 17-point re-election drubbing in 2006.

"Thank you so much, Iowa," said the former Pennsylvania senator, who swapped his trademark sweater vest for a coat and tie to address jubilant supporters in a Des Moines suburb.

The victory strengthened Romney's candidacy heading into next Tuesday's New Hampshire primary, where he enjoys a big lead in the polls and a victory would provide momentum to make him the clear favorite to become the GOP nominee.

Romney, addressing supporters at a downtown hotel before the final results, congratulated Santorum and Ron Paul, who finished third.

"We also feel it's been a great victory for us, as well," he said.

Paul, nearly doubling his Iowa vote from 2008, was a close third. In an otherwise upbeat speech to supporters in the Des Moines suburbs, the Texas congressman said that he and Romney were the only top-tier vote-getters "who can actually run a national campaign and raise the money" _ a clear shot at Santorum.

"We have a tremendous opportunity to continue this momentum," Paul said. But his failure to finish higher disappointed many of his supporters, the dejection evident on the face of his son and political heir, Sen. Rand Paul, R-Ky., who stood behind him onstage.

Despite, or perhaps because of, the wild voter mood swings that produced a revolving cast of front-runners, the caucuses failed to generate the big increase in voter turnout that many Republicans were expecting.

Only slightly more Republicans turned out as in 2008. A clear, cold night was no barrier for Iowa residents. GOP leaders had expected that enthusiasm among party activists would mean increased turnout, like the huge vote that Democrats generated in 2008. But the lack of a compelling social conservative to excite the Christian conservatives who dominate the caucuses, and a late-starting push by Romney, who played down his Iowa campaign until the last six weeks, may have been contributing factors.

Despite the close result, there is no official provision for a recount because no delegates are at stake. The Republican vote was essentially a popularity contest among those who attended, and at some caucus sites there are no paper records of the vote.

The results were a clear setback for a pair of candidates once expected to contend for the nomination _ Perry and Newt Gingrich. Michele Bachmann, who won a high-profile Iowa straw poll last August, was a distant sixth and faces elimination from the race, though she gave no indication in election night comments that she would drop out.

With Romney hoping to put an effective lock on the nomination as soon as the end of this month, the Republican race will now enter a new, more contentious phase.

That seemed clear in Gingrich's withering election night remarks. The former House speaker _ who has been subjected to a fusillade of negative attack ads _ lashed out at Romney, a man he had labeled as a liar in a broadcast interview earlier in the day. Standing before his supporters, his wife Callista at his side, Gingrich called Romney "a Massachusetts moderate who in fact will be pretty good at managing the decay" in America.

Gingrich said Romney had given "no evidence" of an ability to change the culture or politics of the country.

A caucus-night survey of hundreds of Iowans as they entered voting sites across the state showed that Romney, the caucus runner-up during his first presidential try four years ago, split with Santorum the votes of those who identified themselves as Republicans. Romney also was the first choice of those who said they prized business experience over a career in government, a group that made up two-thirds of caucusgoers.

Paul drew strong support from independents and those under 30, many of them first-time caucusgoers. Santorum drew support from social conservatives, who cast about 3 in 5 votes, virtually the same share as in 2008, when Mike Huckabee, an evangelical Christian favorite, was the Iowa winner.

This time, however, religious conservatives splintered. Their inability to coalesce behind a single contender made it possible for Romney to contend for a victory with roughly the same share of the vote he got in 2008.

Paul, meantime, roughly doubled his share of the vote from last time. The iconoclastic congressman from the Houston area, who has been running off and on for president for a quarter-century, was never far from the lead in Iowa.

Despite what could well be the best night of his political career, the 76-year-old candidate remains a distinct long-shot for the GOP nomination.

Paul's isolationism and call for the return of U.S. military forces from overseas deployments has clear appeal to moderates and younger voters. But his dismissal of a threat from Iran's nuclear program poses a potentially insurmountable hurdle for many, if not most, Republican primary voters, who favor a strong U.S. defense posture.

Self-described independents _ deprived of a contest on the Democratic side _ turned out in significantly higher numbers than in 2008. They made up about one-fourth of the vote, according to network entrance polling, compared with 13 percent four years ago.

Nearly half of the independents supported Paul. The popularity of his libertarian views among younger voters _ he speaks favorably of legalizing drugs _ was reflected in the support of nearly half of voters aged 17-29, who made up 15 percent of the caucus electorate, up from 11 percent in 2008.

For Santorum, a long-shot who rode a late surge of support after Perry and Gingrich fell from favor among conservatives, the top-tier finish was a vindication of his old-school approach to the first campaign of the Twitter age. Santorum's financially pinched candidacy followed the classic Iowa playbook _ taking him to all 99 counties over several months.

The former Pennsylvania senator held more than 370 town-hall-style question-and-answer sessions with voters, from the one that attracted a single voter to a number that drew hundreds of supporters in the closing days of the campaign.

Helped by his anti-abortion views, Santorum gained endorsements from several prominent social conservatives, including Bob Vander Plaats, a former GOP gubernatorial candidate, as well as a prominent pastor and a talk-show host in western Iowa, the most conservative part of the state.

Romney had played a coy game with Iowa voters, waiting until the last six weeks to begin an all-out push. He made fewer trips to the state than his main rivals, counting on a stealth effort by his campaign and heavy spending by political action committees that support him.

If Romney were to score back-to-back wins in the first two contests _ something no non-incumbent Republican presidential candidate has ever accomplished _ he'd be positioned as a heavy favorite to gain the nomination.